Electron multiplier



oct. 22, 1940. R. 'COLBERG 2,218,744

ELECTRON MULTIPLI'ER Filed Aug. 24, 1937 2 Sheets-Sheet l 500 4 par/zaar/ MW /nm/ Syvum gmc/nm Oc't. 22, 1940. R, COLBERG ELEcT'RoNMULTIPLIER IIIIIIIIJIIIWIIIII them to the next stage.

Patented Oct. 22, v1.940

ELEo'rRoN MULTIPLIER Rolf Colberg, Berlin-Dahlem, Germany, assignor toFernseh Aktien-Gesellschaft, Zehlendorf,

near Berlin, Germany Application August 24, 1937, serial No. 160,677 IIn Germany September 7,1936

4 Claims.

- 'f This invention relates to an electron multiplier in which highefficiency is to be obtained by simple means. l l

l Electron multipliers are known in which two rows of plane electrodesare placed opposite each other and in which each electrode has a higherpotential than the precedingneighboring electrode. One of theldisadvantages of this arrange-y ment is that lines of force of thepreceding stage end and lines of force of the following stage begin onthe same electrode. That means that secondary electrons liberated fromthe electrode do not always find an vaccelerating field which guidesArrangements are also known in which a magnetic field is provided toguide the electrons so'that the electron path between two electrodes hasthe shape of a half circle. In'this case only one row of electrodes isused for production of secondary electrons, whereas the opposite -rowmerely serves for acceleration'.

In order to guide the primary electrons to the following electrodewithout using a magnetic field, and to secure an accelerating eld forthe secondary electrons liberated at that electrode, it.-

is possible to provide an electron-permeable intermediate yelectrode,for instance a grid which may be held 'at about the-same potential asthe following emitting electrode, so that the elds of subsequent stagesno longer contact each other. Ihe accelerating field of the followingstage can-then cover the entire area of the emitting electrode Aso thatthe secondary electrons are surely drawn' away. 'Ihis invention is basedon recognition of the fact that av corresponding guidance oftheelectrons is also possible without employing a grid or similar structurein the path of the electrons.

ally simple arrangement an emitting electrode'bf' the following stagetakes the place of suchvan lauxiliary electrode so that thedesired eldof Vdistribution is obtain-ed merely a by favorable arrangement of theseelectrodes.r h v Referring to the drawings, Fig. 1 shows a diagram forthe explanation of the effect of the auxiliary electrodes, whereaslFigs. 2 to 5 show several embodiments of the invention.

In Fig. 1, the cathode l` maybe photosensitive. An emitting electrode 2is` held at a potential 400 volts higher. ,'I'he secondary electronsliberated from electrode 2 are accelerated towards the anode 5yand-collected by the latter. The anode 5 carries a potential of 800volts. The arrangement may, for instance, be a figure of rotationsymmetrical. to the axis so that the electrode v 2 has the shape of acon-e and the anode 5 that of a ring. In this case a ring-shapedauxiliary electrode 3 according to the invention is held at apotentialvof :60.0 volts. .Aipotentia'l saddle of about 500 volts isthen obtained between thering 3 and the emitting electrode 2. Thiscauses the-electrons coming from the cathode to travel impacting theelectrode 2 through a range in which they possess a lvelocity higherthan 400 volts. Immediatelyin front of this electrode Aa slightdeceleration takes place which, however, is not harmful because theelectrons still impact with a vvelocity suicient for asecondary-emission ratio greater than unity. .The advantage of thisarrangement ris that an accelerating field is provided'for the secondaryelectrons over the entire area of the emitting electrode 2. This ligureshows equipotential lines according to the potentials 100,y 200, 300volts, and so forth. Some electronpaths are lschematically indicated.

Fig. 2 shows a multistage amplifier in which emitting electrodes 4, 8,l2, I6, 20 and 24 are vheld atpositive potentials of 400, 800, 1200,1600 volts, and so forth, respectively, with respect to the cathode 0.The emitting electrodes consist of plane'plates' perpendicular'to theplane of the drawing. An auxiliary electrode 6, Ill, I4",I i8, 22, 26,respectively, is placed before each emitting electrode, and is held at apotential of 600, 1000, 1400, 1800 volts, and so forth,.respectively.The auxiliary electrodes may have the shape of pins or wires. .Thepotential distribution shown is then obtained, whereby 200, 400,and soforth,'ini,

dicate the potentials of the corresponding equipotential lines. As maybe seen from the drawing, a forking of the potential isobtained thistime in place of a` potential saddle. The emitting electrode 4 is at thesame potential as the forked line 400. lThe electrons coming from thecathode thus possessthe fullvelocity evenbefore trespassing the forkedline, in which they impact the elecv` The space between both contains `atroder 4. comparatively weak acceleratingV eld leading to the nextstage, which however has'no considerable influence upony the electronsbecause of their high velocity. The potential distributionisv by thegrid are eliminated and that the construc-l tion is more simple.

For further simplification, the auxiliaryv elec--l trodes arepreferably. placed somewhat to one side of the row of the emitting4electrodes andprovided Witha higher .potential so that theymay be heldat thesame :potential as an emitting electrode -of'a higher stage andmay be connected with the latter. I'his case is shown in Fig. 3, and

is principally the same arrangement, however, but with cylindri-calemitting electrdes. The cathode 0 and the emitting electrodes 8 andv I6surround the emitting electrodes 4 and I2, which are positioned in theinterior.

' 8, l2', I6', and 20 have the shape of concentric rings and are eachconnected withone ofthe other electrodes. The plate 20 serves as acollector.

ready in Fig. 2. Light is projected through a lens 3i upon aconcentrically arranged cone-shaped mirror 32, which uniformlydistributes it upon the cathode 0. f

Fig. 4 shows a cross-section of a further modication of the embodimentaccording to Fig. 2. The reference vnumbers completely correspond tothose of Fig. 3. However, the electrodes are substantially plane andhave the shape of flat, concentric rings with diameters increasing fromstage to stage. The arrangementis a figure of rotation around the axisAA. vThe electrodes 4 and 8 have a slight curvature at the edge facingthe anode 20. Hereby the eld of the electrodes IB and 20', which areheld at a high potential, is screened off. In lthis manner electrons areheaded for the emitting electrode under a nearly grazing angle whichwould otherwise probably pass the electrode without impacting.

Fig.'5 shows an arrangement in which no auxiliary electrodes arenecessary but in which the desired potential distribution is obtainedmerely by suitable design and arrangement of the electrodes. Thepotentials are again indicated by the reference numbers, the cathode byl0, the emitting electrodes. by 4 and 8, and the collectors by l2. Theelectrodes may be formed as columns perpendicular to the plane of thedrawing with the exception of the electrodes 0 and 4, or also as ringsplaced above and below the plane of the drawing. In the iirst case thecathode may, for instance, be a thermionic cathode which emits only inthe direction of the electrode 4. Equipotential lines in steps of 100volts f are shown, from the shape of which it may be seen that a saddleof about 500 Volts is obtained in front of the. electrode 4, and. asaddle of about 900 volts is obtained in front of the electrodes 8.Thus, an accelerating eld is provided over the entire area ofi'theemitting electrode, which Vdraws 'away .the secondary electrons andguides them to the following electrode where they impact under an angleof about 90 degrees.

'Ihe arrangements of Figs. 1 and 5 may also be modified by moving theelectrodes 2, or 4 and 8, respectively, in the direction of the sourceof electrons, so Lithat they lie exactly in the potential saddle. Theshapes of these electrodes are then made corresponding to theequi-potential surfaces labeled 500 and 900 volts, respectively, and areheld at these potentials. In order to guide possibly all emittedelectrons to the next higher stage the electrodejrnayhave a concavecurva-` ture at the emitting area so that a lens effect occurs. This isshown in the shape of the electrode I, in Fig. 1.

l If a carrier frequency is to be introduced, a high-frequency potentialis applied to one of the electrodes. quency to one or several of theauxiliary electrodes has the advantage that all emitting electrodes maybe connected to ground by condensers. 'Ihis is highly desirable forelimination of interference, so thatl the interference is The auxiliaryelectrodes Vvacuum receptacle in a suitable manner.

The potentials of the electrodesai'e indicated by the reference numbersthe same as al- The application of the high frenot carried throughfurther stages and amplied. An amplification of any stray electronsimpacting the auxiliary electrodes is impossible.

It may be understood that the potentials indicated in the drawings areonly examples. All electrode arrangements are incorporated in a Theelectron multiplier according to the invention may also be combined withanother device, for instance a picture analyzing tube with stationaryscanning aperture, and incorporated in the same vacuum space.

Having thus ldescribed my invention, I claim:

1. An electron multiplier comprising a source of electrons, a secondaryelectron emissive electrodel in electron collecting position withrespect to said cathode and capable when at a positive potential withrespect to said source of normally accelerating an electron from saidsource to said electrode tov reach a velocity of impact at saidelectrode equal to the potential thereof, and another electrode ofsubstantially less exposed surface area than said first electrode,located in a plane intermediate said cathode and said first electrodebut out of the path of travel of said electron, for increasing the rateof acceleration of said electron to thereby cause it to reach its impactvelocity prior to impacting said first- 'mention'ed electrode. i

2. An electron multiplier comprising a source of electrons, asecondary-electron emissive electrode in electron collecting positionwith respect to said source of electrons and capable when at a positivepotential with respect to said source of normally accelerating anelectron from said source to said electrode to re-ach a velocity ofimpact at said electrode equal to the potential thereof, and anotherelectrode in a plane intermediate said cathode and said rst electrodesymmetrically disposed with respect to said rst electrode andlocatedgout of the path ofltravel of said electron, for increasing therate of acceleration of said electron to thereby cause it to reach itsimpact Velocity prior to impacting said first-mentioned electrode.

3. An electro-n multiplier comprising a source of electrons, asecondary-electron emissive electrode in electron-collecting positionwith respect to said cathode, and another electrode located in a planeintermediate said source and said secondary-emissive electrode -butoutside the path of travel of an electron from said'source to saidsecondary-emissive electrode and electrode means for withdrawingelectrons from said secondaryemissive electrode without substantialinterference with electron-guiding iields created by said prior-recitedelectrodes, after energization thereof.

4. An electron multiplier comprising a source of electrons, asecondary-electron emissive electrode in electron-collecting positionwith respect to said cathode and capable when at a positive potentialwith respect to said source, of normally accelerating an electron fromsaid source to said electrode to reach a velocity of impact at saidelectrode equal to the potential thereof, and electrode held-producingmeans in a plane intermediate said cathode` and said rst electrode butout of the path of travel of electrons from said cathode, and means /forwithdrawing secondary electrons from said secondary-emissive electrodewithoutsubstantial interference with the fields produced bysaidprior-recitedelectrodes.`

i ROLF `COLBERG.

